I think even if you put the price difference (and even APS sensors improvements) aside, the FF will always have an upper hand, especially in terms of depth of field and resolving power. The latter can have a limit for human eye, but the former won't ever.

It's pointless to discuss performance w/o considering price. It doesn't matter how good FF is if APS-C is more than adequate at a much lower price (and size).

If performance was all that mattered, computers would still use 8" hard-drives because they'd always have the edge in terms of capacity and cost per byte.